5 Colo. Code Regs. § 1002-32.36
The provisions of C.R.S. 25-8-202(1)(a), (b) and (2); 25-8-203; 25-8-204; and 25-8-402; provide the specific statutory authority for adoption of these regulatory amendments. The Commission also adopted in compliance with 24-4-103(4) C.R.S. the following statement of basis and purpose.
BASIS AND PURPOSE
In this rulemaking hearing, the Commission adopted temporary modifications to the copper acute and chronic standards based upon uncertainty for the portion of Monument Creek from the Tri-Lakes WWFT to the confluence with Fountain Creek (segment 6 of the Fountain Creek sub-basin). The numeric value of the temporary modification Cu(ac) = 36.4 mg/L and Cu(ch) = 24.8 mg/L) is based upon a conservative estimate of a water effect ratio ("WER") of 2.
The temporary modification is applied only to the portion of the segment below the WWTF, since all analytical work has focused on the effects of mixing effluent with the receiving water, a condition that exists only below the WWTF. The expiration date is set to coincide with the next basin wide review and rulemaking hearing.
This temporary modification is based upon uncertainty regarding the appropriateness of the underlying standard, specifically the level of water quality necessary to protect aquatic life. Increased copper discharges from the WWTF have necessitated investigation into both the sources of copper in the Tri-Lakes system and the appropriateness of the standard. Tri-Lakes will continue its investigation including source control, water effect ratios and biotic ligand modeling to determine an appropriate WER. Consistent with the sampling plan for quarterly and monthly data collection, the seasonal aspects of potential copper toxicity and the downstream extent of the WER will also be explored. The study will be completed in time for the basin-wide Issues Formulation Hearing in November 2006. If the study is completed before that time, a hearing may be requested before the basin-wide hearing.
PARTIES/MAILING LIST STATUS FOR NOVEMBER, 2004 RULEMAKING HEARING
5 CCR 1002-32.36